<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var first = prompt('请输入第一个数');
        var second = prompt('请输入第二个数');
        var sum = parseFloat(first) + parseFloat(second);
        alert('和为' + sum);
    </script>

</head>
<body>
    
</body>
</html>